This invention relates primarily to turbomachinery blading and, more particularly, to an improved tip cap configuration for a hollow turbomachinery blade and a method of making such a configuration.
It is well known that significant increases in gas turbine engine performance, in terms of thrust or work output per unit of fluid input, can be obtained by increasing the turbine inlet temperature of the motive fluid or hot gas stream flowing through the engine. It is also recognized that one major limitation on turbine inlet temperature is that which is imposed by the turbine blade temperature capability. In an effort to extend turbine blade capabilities, numerous complex turbomachinery blade structures have been proposed which employ one or more modes of cooling using fluid extracted from the gas turbine engine compressor.
One such mode of cooling which is becoming prevalent is the provision of impingement inserts within an internal cavity defined by a hollow body portion of the turbomachinery blade. Coolant is delivered to the interior of such an insert and is expelled through a multiplicity of small holes against an internal wall of the turbomachinery blade, thereby cooling that portion of the turbomachinery blade which is exposed to the hot gas stream.
In order to permit insertion of the impingement inserts into the interior of the turbomachinery blade, many such blades are provided with open tip ends. As is known to those skilled in the art, in order to maximize turbine efficiency, it becomes necessary to minimize the amount of cooling air which is expended in cooling each component. For this reason, it has become necessary to seal the tip ends of the blades in order to prevent cooling fluid from being wastefully discharged into the gas stream. In many prior art designs, the open tip end of the blade is sealed by means of a tip cap which is joined to the blade in a suitable manner. While a number of alternative methods have been proposed in the past for joining the tip cap to the blade, none of these methods has proven universally acceptable for numerous reasons. When one considers that these tip caps must operate in an environment where they are subjected to centrifugal forces on the order of 100,000 times the normal gravitational force and metal temperatures in excess of 1500.degree. F., it becomes easy to envision why no single method of joining the tip cap to the blade has proven universally acceptable.
When one further considers the fact that the tip cap is inserted in an airfoil-shaped blade and that any distortion in the shape of the airfoil at its tip end can greatly reduce the aerodynamic efficiency of the blade, the problems of joining the tip cap to the blade increase. The problems are even further complicated when cooling requirements for that portion of the blade tip which extends above the tip cap are considered.